JUST got the job notice that the ghost and other things was around.
It was not in the small books, but the bookshelf. Climbing the stairs I saw a ghost queued, from what I remember that happened after activating the books, but this time it happened before I got to activating the bookshelf. The sim reaped the ghost and it worked. So it looks like the ghost "scare" (I'm guessing) can interrupt the reap section of that.
Okay, reloaded the same modded save, the reaping worked again. The ghost "scare" showed up and stopped the sim from getting the ghost out of the bookshelf, but it did reap it the same way again, so I'm not entirely sure what happened with the standalone books on the upper floor, but perhaps something else was causing the sim to not complete the reap section, as something caused it to "X" out.
Third try of the same save, I tried to X out of it after the ghost was evicted from the bookshelf and it did, but right atop it was "Scared by ghost", so quite possible the ghost scared the sim mid-activation, because it did "X" out of it the original 2 times it didn't work from the standalone books (near the stair exit upstairs). Perhaps as a means of "fixing this", have an extra activation on that ghost that lets you finish the situation (and maybe make it run around causing havoc).
Didn't think Reapers could be scared by ghosts?
I can try an unmodded save of it, but with it completing 2 times in a row and me canceling it so it wouldn't on the third, means that the first 2 were getting cancelled externally, so probably better to have an extra interaction to chase after the ghost if it "got loose again".
The Sims Team